The invention relates to a display system comprising a plurality of light-emitting elements which can be driven in accordance with image information to be displayed and are aligned with respect to each other in a well-defined manner, further comprising a rotating element having at least one reflecting surface, and an image-forming optical system for converting the light modulation generated by the light-emitting elements into an image.
A display system of the type described in the opening paragraph is known from, for example, U.S. Pat. No. 4,934,773. The display system described in this patent comprises a plurality of light-emitting elements to which image information is applied. To this end, the elements are driven selectively. The light-emitting elements, which are arranged in, for example, a linear array, are scanned by means of a vibratory mirror. This results in the projection of a plurality of picture elements on selected positions of the mirror. Since the mirror moves and, synchronized with each movement, drives the picture elements with different image information, a two-dimensional image is obtained.
It is an object of the present invention to provide a display system having an improved performance as compared with the display system of the type described in the opening paragraph.
To this end, the display system according to the invention is characterized in that the at least one reflecting surface encloses an angle with the plane in which the axis of rotation of the reflecting element is situated, the axis of rotation of said element being substantially perpendicular to the light path of the light-emitting elements.
The rotating element may be, for example, a reflecting element with a plane rotating between two extreme angles around an axis.
The rotating element may also comprise more than one reflecting surface. In this case, each light-emitting element is projected at a number of positions corresponding to the number of reflecting surfaces, due to the angle which is enclosed between the surfaces and the plane in which the axis of rotation is situated. The result is that the number of light-emitting elements can be reduced, or the same number of light-emitting elements can yield a larger number of image lines.
An embodiment of the display system according to the invention is characterized in that the reflecting surfaces of the rotating element are deformable in a direction substantially perpendicular to the direction of rotation.
Due to deformation of the reflecting surfaces in said direction, a magnification in a direction perpendicular to the direction in which the reflecting surfaces perform their scanning movement is made possible. Thus, this provides magnifications in two directions which are independent of each other.
A further embodiment of the display system according to the invention is characterized in that the image-forming optical system further comprises at least one deformable mirror.
This element provides an extra possibility of adapting the shape of the image before it is projected.
A simple embodiment of the display system according to the invention is characterized in that the light-emitting elements are arranged in a linear array.
A further embodiment of the display system according to the invention is characterized in that the number of light-emitting elements for at least one color is smaller than for the other colors.
By choosing the suitable number of light-emitting elements per color, the resolution is improved considerably.
The human eye has a different sensitivity to the spatial resolution of the different colors. This means that, for those colors for which the sensitivity is lower than for another color, it is sufficient to use fewer light-emitting elements for the color for which the sensitivity is lower.
A further embodiment of the display system according to the invention is characterized in that the light-emitting elements are arranged in linear arrays, and the arrays of the same color are longitudinally offset with respect to each other.
This embodiment relates to a color display system in which the light-emitting elements are arranged in linear arrays and in which the resolution is improved. Two successive arrays of the same color are longitudinally offset with respect to each other. Two successive arrays are preferably offset through half a pitch between the light-emitting elements.
A further embodiment of the display system according to the invention is characterized in that the linear arrays are made of one piece.
This is realized by cutting a one-piece array from one wafer. Advantages are, inter alia, a simple, compact implementation of the array and the omission of mutual positioning and alignment of discrete elements.
A further embodiment of the display system according to the invention is characterized in that the display system is provided with a number of light guides corresponding to the number of light-emitting elements.
By making use of, for example, optical fibers, the array of picture elements to be scanned can be made smaller in the case of relatively large light-emitting elements. Moreover, transport of light through an optical fiber allows great freedom of positioning the light-emitting elements.
A further embodiment of the display system according to the invention is characterized in that the light-emitting elements are pulsed lasers, in which the image information for two adjacent light-emitting elements can be supplied at different instants within the period of forming the image.
In this way, crosstalk between adjacent picture elements is reduced considerably.
A further embodiment of the display system according to the invention is characterized in that a plurality of light-emitting elements jointly constitutes a single picture element, the display system comprising feedback means for driving the light-emitting elements within a picture element to a predetermined drive level per picture element.
Each picture element consists of a number of light-emitting elements which receive the same image information per picture element. The drive level is determined for each picture element. The feedback means ensures that, with reference to the number of functioning light-emitting elements, this drive level within the same picture element is achieved for each picture element. In this way, the risk of non-functioning or malfunctioning picture elements in the image is reduced considerably.